Purification of refractory metals



United States Patent C) PURIFICATION OF REFRACTORY METALS Donald F. Taylor, Waukegan, Robert L. Baughman, Zion, and Leonard F. Yntema, Wadsworth, Ill., assignors to Fausteel Metallurgical Corporation, a corporation of New York No Drawing. Application October 14, 1957 Serial No. 689,769

15 Claims. (Cl. 75-200) This invention relates to a method of sintering and purifying refractory metals and particularly in treating a refractory metalwhich contains as an impurity an amount of a metal which prevents the resulting sintered refractory metal from being sufficiently ductile to be Worked, whereby such an embrittling quantity of metal is removed during sintering so that the resulting sintered refractory metal is sufliciently ductile to be worked.

This application is a continuation-in-part of United States patent application Serial Number 239,395, filed July 30, 1951, now abandoned, and our copending United States patent application Serial Number 545,554, filed November 7, 1955, now abandoned.

In the case of refractory metals, such as tantalum,

columbium, tungsten, molybdenum and the like, it is common practice to press the refractory metal powder in the form of a bar and then sinter the pressed bar. In the process of making the refractory metal powder, the powder, on occasion, contains as an impurity a metal, such as for example aluminum, in an amount which prevents the resulting sintered refractory metal from being sufficiently ductile to be Worked, and the embrittling quantity of such metal cannot be removed even when sintering under high vacuum conditions over long periods of time.

In the case of tantalum, for example, the amount of metal impurity which does not volatilize at the sintering temperature of the refractory metal and which causes embrittlement is in excess of about 0.5% by weight, and may be as much as about 2% by weight. For reasons un known to us, when the metal impurity is present in an amount below about 0.5% by weight it does not cause embrittlement. This is also true for such other refractory metals as columbium, molybdenum and tungsten. When these refractory metals contain embrittling amounts of metal impurity, the metal impurity should be reduced to amounts below about 0.5% and preferably to amounts below about 0.2%, thereby eliminating the embrittling effect. It is preferred that the metal impurity be reduced to about 0.02% by weight or less.

In general, it is desirable to make a preliminary test to determine whether the refractory metal contains an embrittling quantity of a metal impurity which does not volatilize at the sintering temperature of the refractory metal. Such a test comprises forming a test bar from the refractory metal powder containing the said metal impurity in the form of a compact under 15 tons/in. pressure; heating the compact at the sintering temperature of the refractory metal to form a sintered bar; and then attempting to work the bar under normal procedures such as, for example, rolling. If the bar contains an embrittling quantity of the said metal impurity, it will break upon rolling and the remainder of the powder of the refractory metal should then be treated in accordance with our new method set forth herein.

We have discovered that under such conditions the embrittling quantity of metal impurity, such as aluminum, may be removed by mixing a powder of the refractory metal, such as tantalum, columbium, molybdenum, tungice sten and the like, containing this embrittling quantity of the metal impurity with a small proportion of a powder of a third metal, such as for example copper, silver, or gold, which volatilizes at the sintering temperature of the refractory metal, does not alloy with the refractory metal, and volatilizes off with the embrittling quantity of the metal impurity to render the sintered metal sufliciently ductile to be worked.

Following is a detailed description of our new method with reference specifically to the sintering and purification of tantalum and columbium metals which contain in the powder form as an impurity an amount of aluminum which prevents the resulting sintered tantalum or columbium metal from being sufliciently ductile to be worked, whereby such an embrittling quantity of aluminum is removed during sintering so that the resulting sintered tantalum or columbium metal is sufliciently ductile to be worked.

It is to be understood that the new method is applicable to other refractory metals, such as molybdenum, tungstem, and the like, as Well as tantalum and columbium which contain an embrittling quantity of a metal impurity other than aluminum in which a third metal volatilizes at the sintering temperature of the refractory metal, does not alloy with the refractory metal and volatilizes ofi with the embrittling quantity of the metal impurity.

In the case of tantalum or columbium, these metals cannot be recovered from tantalite, columbite and similar ores by a smelting process, nor can they be obtained by a reduction of the oxides with hydrogen. Under the present process these ores are fused with caustic soda to convert the tantalum or columbium into crude sodium tantalate'and sodium columbate mixed with a number of impurities. After cooling, the fused mass is crushed and the water soluble impurities removed by leaching with water. The acid soluble impurities are then removed by treating the mass with hot hydrochloric acid. This converts the sodium tantalate and sodium columbate into insoluble tantalic and columbic acids. This mixture of acids is then dissolved in hot hydrofluoric acid. Potassium carbonate is then added to form the double salts, potassium tantalum flouride and potassium columbium oxyfluoride. The hot solution is then cooled. The potassium tantalum fluoride crystallizes out leaving the potassium columbium oxyfluoride in solution. The

crystallized tantalum salt is separated from the solution,

washed and dried and the columbium salt is recovered from the solution. The pure tantalum and columbium metals are obtained from the double fluorides by electrolysis of the respective fused salts, the metal becoming dispersed as fine grains or powder in the salt mass as electrolysis progresses. After electrolysis, the salt mass is crushed and the metal recovered from the crushed mass.

The electrolysis of the fused tantalum or columbium salts is a costly operation. In our co-pending United States patent applications, Serial Number 689,766, filed October 14, 1957, and Serial Number 682,287, filed September 6, 1957, we have disclosed and claimed new methods of recovering the tantalum or columbium pow der which omit the costly electrolysis step. These meth ods include treating, for example potassium tantalum fluoride or potassium columbium oxyfluoride, with (1) aluminum or (2) an excess of an alloy of aluminum and copper, silver or gold.

In the first of these methods, i.e., the treatment of the double salt of tantalum or columbium with aluminum, the aluminum reacts with the double salt to form an intermetallic compound or alloy or columbium or tantalum and the aluminum. This intermetallic compound or alloy is then reacted with copper, silver or gold.

When copper is used, an aluminum-copper alloy is formed together with tantalum or columbium in a reaction mixture in which the tantalum or columbium is in the form of finely divided grains dispersed throughout the mixture and in a substantially pure state. The tantalum or columbium grains are then separated from the reaction mixture.

In the other method, the reaction of an excess of aluminum-copper alloy with potassium tantalum fluoride or potassium columbium oxyfluoride, a reaction mixture is formed which includes an alloy of aluminum and copper; tantalum or columbium in the form of finely divided particles or grains dispersed throughout the metal portion of the reaction mixture in a substantially pure state; and aluminum fluoride and potassium fluoride as slag.

Under certain conditions, the resulting tantalum or columbium powder separated from the above reaction mixtures has been found to contain an amount of aluminum which prevents the resulting sintered tantalum or columbium from being sufiiciently ductile to be worked, even when the sintering is conducted for a long period of time under high vacuum conditions. The amount of aluminum present may be as much as about 2% by weight. If the amount of aluminum exceeds about 0.5% by weight the refractory metal will be too brittle to be worked.

We have discovered that upon adding and mixing with finely divided particles of such tantalum and columbium powder, finely divided copper, silver or gold and sintering the columbium or tantalum powder containing the fienly divided particles of copper, silver or gold at a temperature of at least the sintering temperature of tantalum or columbium, the copper, silver or gold volatilizes oif with the embrittling quantity of aluminum to render the sintered metal sufficiently ductile to be worked. The quantity of aluminum in the refractory metal powder is thus reduced to an amount less than about 0.5% and usually to an amount less than about 0.2%. The quantity of aluminum is often reduced to about 0.02% or less. It is preferred that the amount of aluminum be reduced to less than about 0.2%, but even as much aluminum as up to about 0.5 may be present without rendering the refractory metal too brittle to be worked.

The addition of a small amount of copper, silver or gold, i.e., an amount of copper, silver or gold up to about 10% by weight, and usually from about 1% to 5%, to the tantalum or columbium powders containing an embrittling quantity of aluminum of from about 0.5 to about 2% by weight or more, results in the removal of the embrittling quantity of aluminum during sintering so that the resulting sintered bar of columbium or tantalum is comparable to those produced commercially by the usual production methods. The copper, silver or gold does not alloy with tantalum or columbium and is volatilized at temperatures appreciably below the sintering temperature of these metals, i.e., about 2000 C. to 2100 C. for tantalum and about 1800 C. for columbium.

The copper, silver or gold metal powder appears to perform a two-fold function. Each insures a reduction of an embrittling quantity of aluminum-tantalum or aluminum-columbium intermetallic compound or alloy remaining in the powder to tantalum or columbium and an aluminum-copper alloy which is readily volatilized. In addition, the copper, silver or gold also functions to impart and maintain suflicient porosity during the initial stages of the sintering operation so as to permit volatilization of the copper, silver or gold and removal of the embrittling quantity of aluminum therewith. The sintering procedure may be in accordance with conventional sintering practice.

By reduction of the quantity of aluminum-tantalum or aluminum-columbium intermetallic compound or alloy and by maintaining suflicient porosity to permit volatilizaion of the added copper, silver or gold along with the embrittling quantity of aluminum, the embrittling quantity of aluminum is removed, rendering the resulting sintered bar comparable in physical and mechanical characteristics to a sintered bar produced by conventional production methods when employing tantalum or columbium powder which does not contain an embrittling quantity of aluminum. Following are examples illustrative of our new method:

Tantalum powder is prepared from potassium tantalum fluoride by first reducing the double fluoride with aluminum, followed by reaction of the resulting aluminumtantalum intermetallic compound or alloy with copper. The resulting ingot includes an aluminum-copper alloy having tantalum particles dispersed therethrough. The tantalum is recovered from the ingot by treating the ingot with hydrochloric acid and Washing and drying the tantalum powder. This powder contains the following impurities:

Percent Carbon 0.22

Iron 0.05 Tungsten 0.032 TiO 0.01 sio 0.70 Copper 0.70 Aluminum 0.87

Following are examples of bars made from this powder which are pressed, sintered and cold rolled:

Bar 1 69.6 grams of the tantalum powder is pressed in the form of a bar under 55 tons per square inch pressure. This pressed bar has the following dimensions:

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 2.5 microns. It requires minutes to heat the bar to a temperature of 2010 C. Upon reaching this temperature, the bar bulges and a portion melts.

Results.The hardness of this bar after sintering is Rockwell E=116. (It is to be noted that a tantalum bar having a hardness of R =116 is much too hard to be cold worked.)

Analysis of the sintered bar shows that the carbon, SiO and copper contents are reduced materially: Carbon to about 0.00%, SiO- to about 0.15%, and copper to about 0.014%. The tungsten content is reduced slightly (to about 0.025%). However, the aluminum content in the sintered bar is substantially the same as was present before sintering.

Upon attempting to cold roll the sintered bar, it breaks.

Bar 2 64.6 grams of the tantalum powder is pressed in the form of a bar under 15 tons/m This pressed bar has The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 3.0 microns. It is heated to a temperature of about 2100 C., held at this temperature for 15 minutes, heated to a temperature of 2175 C. and held at this temperature for minutes, heated to a temperature of 2300 C. and held at this temperature for 5 minutes, and then heated to a temperature of 2425 C., at which temperature the bar bulges and a portion melts.

Results.The hardness of this sintered bar is R =95. (It is to be noted that a tantalum bar having a hardness of R =95 is much too hard to be cold worked.)

Analysis of the sintered bar shows that the carbon, SiO and copper contents are reduced materially: Carbon to about 0.00%, SiO to about 0.23%, and copper to about 0.015%. The tungsten content is reduced slightly (to about 0.027%). However, the aluminum content in the sintered bar is substantially the same as was present before sintering.

Upon attempting to cold roll the sintered tantalum bar, it breaks.

Bar 3 62.5 grams of the tantalum powder is pressed in the form of a bar under tons/m This pressed bar has the following dimensions:

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 0.9 micron, as follows: It is heated slowly to a temperature of about 2100 C. and held at this temperature for 85 minutes, and then heated to a temperature of 2320 C., at which temperature the bar bulges and a portion melts in much the same manner as Bar 2.

Results-The hardness of this bar after sintering is R =94. (It is to be noted that a tantalum bar having a hardness of R =94 is much too hard to be cold worked.)

Analysis of the sintered bar showed that the carbon, SiO and copper contents are reduced materially: Carbon to about 0.00%, SiO to about 0.17%, and copper to about 0.015%. The tungsten content is reduced slightly (to about 0.026%). However, the aluminum content in the sintered bar is substantially the same as was present before sintering.

Upon attempting to cold roll the sintered bar, it breaks.

Bar 4 63.2 grams of the tantalum powder is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 0.9 micron. It is heated to a temperautre of 2250 C. and held at this temperature for 40 minutes. At the end of this period the bar bulges.

Results.The hardness of this bar after sintering is R =96. (It is to be noted that a tantalum bar having Bar 5 64.4 grams of a powder mix consisting of of the tantalum powder and 5% copper powder is pressed in the form of a bar under 15 tons/in. pressure.

This pressed bar has the following dimensions:

Thickness: Inches End 0.269 Center 0.261 End 0.258

Width:

End 0.25 8 Center 0257 End 0.258 Length 6.03

The resulting pressed bar is sintered under a vacuum condition of 0.9 micron. This bar is heated to a temperature of 2090 C. and held at this temperature for minutes. The resulting sintered bar is cold rolled in one direction at right angles to the length of the bar in a single pass, being reduced 30% in thickness (to 0.160). The cold rolled bar is then resintered at a temperature of 2140 C. for 148 minutes. Following the second sinter, the bar is then cold rolled in one direction at right angles to the length of the bar to a thickness of 0.004.

Results-Analysis of the bar after the second sinter shows that it contains the following impurities:

Percent Carbon 0.00 Iron 0.030 Tungsten 0.031 Ti0 0.010 Si0 0.020 Copper 0.013 Aluminum 0.085

The resulting tantalum sheet of 0.004" thickness has no cracks and is sufficiently ductile to be cold rolled into foil.

Bar 6 To 60.61 grams of the tantalum powder is added 3.19 grams of copper powder (5%). After thoroughly mixing the tantalum-copper powder mix, 63.8 grams of this mix is pressed in the form of a bar under 15 tons per square inch pressure.

The pressed bar has the following dimensions:

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 0.8 micron. It is heated at 2090 C. for 180 minutes. The bar is then cold rolled in one direction parallel to the length of the bar to a thickness of 0.160" in a single pass (a reduction of 30%). The bar is then sintered a second time at a temperature of 2140 C. for approximately 148 minutes,

7 following which it is cold rolled in one direction parallel to the length of the bar to a thickness of 0.004.

Results.The bar after the second sinter contains the following impurities:

Percent Carbon 0.00 Iron 0.033 Tungsten 0.021 TiO 0.01 Si 0.28 Copper 0.019 Aluminum 0.150

The tantalum sintered bar is sufliiciently ductile to be worked under normal conditions.

Bar 7 To 61.28 grams of the tantalum powder, 3.22 grams of copper powder is added. After thoroughly mixing the tantalum-copper powder mix, 64.5 grams of the mix is pressed in the form of a bar under tons/in.

The resuting pressed tantalum bar is sintered at 2090 C. for 180 minutes. Following sintering, the bar is cold rolled in a direction parallel to its length to about 0.060 in thickness, then sintered a second time at a temperature of 2140 C. for 148 minutes, following which the resulting bar is cross rolled (cold) to a thickness of 0.004".

Results-The bar after the second sinter has the following impurities:

Percent Carbon 0.00 Iron 0.012 Tungsten 0.023 Ti0 0.01 SiO 0.13 Copper 0.0135 Aluminum 0.065

The sintered bar is sufficien-tly ductile to be worked under normal conditions and the 0.004" thick cold rolled sheet is ductile enough to be cold rolled to foil.

Bar 8 To 74.1 grams of the tantalum powder is added 3.90 grams of copper powder (5%). After thoroughly mixing the tantalum-copper powder mix, 78.0 grams of the mix is pressed in the form of a bar under 15 tons per square inch pressure.

The pressed bar has the following dimensions:

Thickness: Inches End 0.1 10 Center 0.110 End 0.1 10

Width:

End 0.625 End 0.625 Center 0.625 Length 7.25

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 0.8 micron. It is heated to a temperature of 2100 C. and held at this temperature for 135 minutes. The bar is then reduced 30% in thickness by cold rolling (one pass of the rolls), following which it is sintered a second time for 120 8 minutes at 2100 C. under a vacuum condition of 0.7 micron.

The bar is then cold rolled in one direction at right angles to the length thereof to form a sheet 0.004"

thick.

Results-This bar, after the second sinter, has the following impurities:

Percent Carbon 0.00 Iron 0.017 Tungsten 0.23 Ti0 0.01 SiO 0.01 Copper 0.009 Aluminum 0.005

This sintered bar is sufficiently ductile to be Worked under normal conditions and the cold rolled sheet of 0.004 thickness is sufficiently ductile to be rolled to foil.

Bar 9 To 74.29 grams of the tantalum powder is added 3.91 grams of copper powder (5%). After thoroughly mixing the tantalum-copper powder mix, 78.2 grams of the mix is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

Thickness: Inches End 0.115

Center 0.123

End 0.124 Width:

End 0.628

Center 0.630

End 0.630 Length 7.25

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 0.7 micron for 135 minutes at 2100 C. The bar is then reduced 30% in thickness by rolling (one pass of the rolls), following which the bar is sintered a second time for minutes at 2100 C. The bar is then cross rolled to 0.004" thick sheet.

Results.-The bar, after the second sinter, has the following impurities:

Percent Carbon 0.00 Iron 0.026 Tungsten 0.027 TiO 0.010 SiO 0.010 Copper 0.0096 Aluminum 0.020

The hardness of the bar after the first sinter is R =73 and after the second sinter R =76.

The bar is sufficiently ductile to be worked under normal conditions and the cold rolled sheet of 0.004" thickness is capable of being cold rolled to foil.

Bar 10 To 86.13 grams of the tantalum powder is added 0.87 gram of copper powder (1% After thoroughly mixing the tantalum-copper powder mix, 87.0 grams of the mix is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

Thickness: Inches End 0.103

Center 0.11 1

End 0.105 Width:

End 0.634

Center 0.636

End 0.634 Length 7.5

Percent Carbon 0.00 Iron 0.025 Tungsten 0.025 TiO 0.01 SiO 0.01 Copper 0.005 Aluminum 0.034

This bar is sufiiciently ductile to be worked under normal conditions and cold rolled readily to a sheet thickness of 0.005".

Bar 11 82.9 grams of a powder mix consisting of 95% of the tantalum powder and copper powder is pressed in the form of a bar under 15 tons/in. pressure. The

pressed bar has the following dimensions:

Thickness: Inches End 0.108 Center 0.114 End 0.110

Width:

End 0.636 Center 0.637 End 0.636 Length 7.5

The resulting pressed tantalum bar is sintered at 2100 C. for 120 minutes under a vacuum condition of 0.7 micron. This bar is then cold rolled to 70% of its thickness and sintered a second time at 2100 C. for 120 minutes under a vacuum condition of 0.6 micron. The bar is then cold rolled to a sheet 0.005" thick.

Results.--The bar, after the second sinter, has as impurities:

Percent Carbon 0.00 Iron 0.025 'Iilngsten 0.025 TiO 0.01 Si0 0.01 Copper 0.005 Aluminum 0.01

The sintered bar is sufiiciently ductile to be Worked under normal conditions and is cold rolled readily to a sheet 0.005" thick.

Bar 12 84.7 grams of a powder mix consisting of 90% of the tantalum powder and copper powder is pressed in The pressed bar is sintered for 120 minutes at 2100 C. under a vacuum condition of 0.6 micron. The resulting sintered bar is then cold rolled to 70% of its thickness, following which it is sintered a second time at 2100 C. for 128 minutes under a vacuum condition of 0.6 micron. Following the second sinter, the bar is cold rolled to a sheet having a thickness of 0.0045". This 0.0045" thick sheet is annealed at 1400 C. for 10 minutes and then cold rolled to 0.0019" thick. After cleaning, it is pack rolled to a sheet 0.007" thick.

Results.-The bar, after the second sinter, contains the following impurities:

Percent Carbon 0.005 Iron 0.024 Tungsten 0.023 TiO 0.01 SiO 0.01 Copper 0.005 Aluminum 0.020

The second sintered bar is sufliciently ductile to be worked under normal conditions and the resulting sheet from this bar exhibits excellent strength and ductility.

Bar 13 About 70 grams of a mixture of the tantalum powder and 5% copper powder is pressed into a bar 6" in length and A square in cross section at a pressure of 15 tons/m The bar is sintered under a vacuum condition of 0.7 micron at a temperature of about 2090 C. for about 3 hours. The sintered bar was found to be sound and malleable. The bar is then cold rolled to 70% of its thickness in a single pass and then re-sintered at a temperature of about 2150 C. for approximately 2% hours under a vacuum condition of 0.8 micron. After the second sintering operation, the bar is satisfactorily cold rolled into a sheet having a thickness of 0.004".

The sheet after completion of the rolling operation The bar after the second sinter is sufliciently ductile to be worked under normal conditions and the resulting sheet from the bar exhibits excellent strength and ductility.

Bar 14 Approximately 70 grams of a mixture of the tantalum powder and 5% copper powder is pressed into a bar 7.25" in length and having a cross section of approximately 0.1" x 0.625" at a pressure of about 15 tons/m The bar is sintered at about 2100 C. for 2% hours under a vacuum condition of about 0.8 micron. The bar is then cold rolled to 70% of its thickness in a single pass, following which the bar is then re-sintered at 2100 C. for about 2 hours under a vacuum condition of 0.7 micron. The bar is then cold rolled into a sheet having a thickness of 0.004".

The 0.004" thick sheet contained the following im- To 86.13 grams of the tantalum powder is added 0.87 gram of silver powder (1%). After thoroughly mixing the tantalum-silver powder mix, 87.0 grams of the mix is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

1 1 Thickness: Inches End 0.103 Center 0.111 End 0.105 Width:

End 0.634 Center 0.636 End 0.634 Length 7.5

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 0.7 micron for 120 minutes at a temperature of 2100 C. under a vacuum condition of about 0.7 micron. The resulting bar is then cold rolled to a sheet of 0.005" thickness.

Results-The bar, after the second sinter, has the following impurities:

Percent Carbon 0.00 Iron 0.025 Tungsten 0.025 TiO 0.01 SiO 0.01 Silver 0.005 Aluminum 0.034

This bar is sufficiently ductile to be worked under normal conditions and cold rolled readily to a sheet thickness of 0.005".

Bar 16 82.9 grams of a powder mix consisting of 95% of the tantalum powder and 5% silver powder is pressed in The resulting pressed tantalum bar is sintered at 2100 C. for 120 minutes under a vacuum condition of 0.7 micron. This bar is then cold rolled to 70% of its thickness and sintered a second time at 2100 C. for 120 minutes under a vacuum condition of 0.6 micron. The bar is then cold rolled to a sheet 0.005" thick.

Results.-The bar, after the second sinter, has as impurities:

Percent Carbon 0.00 Iron 0.025 Tungsten 0.028 TiO 0.01 SiO 0.01 Silver 0.005 Aluminum 0.01

The sintered bar is sufiiciently ductile to be worked under normal conditions and is cold rolled readily to a sheet 0.005" thick.

Bar 17 84.7 grams of a powder mix consisting of 90% of the tantalum powder and silver powder is pressed in the form of a bar under tons/in. pressure. The

pressed bar has the following dimensions:

Thickness: Inches End 0.109 Center 0.115 End 0.113

12 Width:

End 0.634 Center 0.636 End 0.634 Length 7.5

The pressed bar is sintered for 120 minutes at 2100 C. under a vacuum condition of 0.6 micron. The resulting sintered bar is then cold rolled to 70% of its thickness, following which it is sintered a second time at 2100 C. for 128 minutes under a vacuum condition of 0.7 micron. Following the second sinter, the bar is cold rolled to a sheet having a thickness of 0.0045". This 0.0045" thick sheet is annealed at 1400 C. for 10 minutes, and then cold rolled to 0.0019" thick. After cleaning, it is pack rolled to a sheet 0.0007" thick.

Results.The bar, after the second sinter, contains the following impurities:

Percent Carbon 0.005 Iron 0.024 Tungsten 0.023 TiO 0.01 SiO 0.01 Silver 0.005 Aluminum 0.020

The second sintered bar is sulficiently ductile to be worked under normal conditions and the resulting sheets from this bar exhibit excellent strength and ductility.

Bar 18 To 86.13 grams of the tantalum powder is added 0.87 grams of gold powder 1%). After thoroughly mixing the tantalum-gold powder mix, 87.0 grams of the mix is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

Thickness: Inches End 0.103 Center 0.11 1 End 0.105

Width:

End 0.634 Center 0.63 6 End 0.634 Length 7.5

Percent Carbon 0.00 Iron 0.025 Tungsten 0.025 TiO 0.01 z 0.01 Gold 0.005 Aluminum 0.034

This bar is sufliciently ductile to be worked under normal conditions and cold rolled readily to a sheet thickness of 0.005".

Bar 19 82.9 grams of a powder mix consisting of of the tantalum powder and 5% gold powder is pressed in the form of a bar under 15 tons/in. pressure. The pressed bar has the following dimensions:

The resulting pressed tantalum bar is sintered at 2100 C. for 120 minutes under a vacuum condition of 0.7 micron. This bar is then cold rolled to 70% of its thickness and sintered a second time at 2100 C. for 120 minutes under a vacuum condition of 0.6 micron. The bar is then cold rolled to a sheet 0.005" thick.

Results.The bar, after the second sinter, has as impurities:

Percent Carbon 0.00 Iron 0.025 Tungsten 0.025 Ti 0.01 SiO 0.01 Gold 0.005 Aluminum 0.01

The sintered bar is sufiiciently ductile to be worked under normal conditions and is cold rolled readily to a sheet 0.005" thick.

Bar 20 84.7 grams of a powder mix consisting of 90% of the tantalum powder and gold powder is pressed in the form of a bar under tons/in. pressure. The pressed bar has the following dimensions:

The pressed bar is sintered for 120 minutes at 2100 C. under a vacuum condition of 0.6 micron. The resulting sintered bar is then cold rolled to 70% of its thickness, following which it is sintered a second time at 2100 C. for 128 minutes under a vacuum condition of 0.6 micron. Following the second sinter, the bar is cold rolled to a sheet having a thickness of 0.0045". This 0.0045" thick sheet is annealed at 1400 C. for 10 minutes, and then cold rolled to 0.0019 thick. After cleaning, it is pack rolled to a sheet 0.0007" thick.

Results.The bar, after the second sinter, contains the following impurities:

The second sintered bar is sufliciently ductile to be worked under normal conditions and the resulting sheets from this bar exhibit excellent strength and ductility.

In addition to the foregoing bars, a 21st bar is formed as follows:

Bar 21 73.2 grams of tantalum powder is pressed in the form of a rectangular-shaped bar under 55 tons/in. pressure. This tantalum powder does not contain any aluminum, copper, gold or silver, but has the following impurities:

Percent Carbon 0.015 Iron 0.018 Tungsten 0.03 TiO 0.05 Si0 0.05

The pressed bar has the following dimensions:

Thickness: Inches End 0.263 Center 0.265 End 0.267

Width:

End 0.258 Center 0.257 End 0.25 8 Length 6.03

The resulting pressed tantalum bar is sintered under a vacuum condition of approximately 0.8 micron at a temperature of about 2330 C. for minutes.

The bar is then cold rolled to a sheet 0.004" thick.

Results.The sintered bar contains the following impurities:

Percent Carbon 0.00 Iron 0.015 Tungsten 0.028 TiO 0.05 Si0 0.05

The sintered tantalum bar is sufficiently ductile to be cold worked under the normal conditions and the sheet formed from the bar is capable of being cold rolled to foil.

Columbium powder is prepared from potassium columbium oxyfluoride by first reacting the double fluoride with aluminum. The resulting aluminum-columbium intermetallic compound or alloy is then reacted with copper to form an ingot. The resulting ingot includes an aluminumcopper alloy having columbium particles dispersed therethrough. The columbium is recovered from the ingot by treating the ingot with hydrochloric acid and washing and drying the columbium powder. This powder contains the following impurities:

Percent Carbon 0.18 Iron 0.06 Tungsten 0.02 TiO 0.02 Si0 0.60 Copper 0.71 Aluminum 1.24

Following are examples of pressed, sintered and cold rolled columbium bars made from the above described powder Bar 22 To 43.07 grams of the columbium powder is added 0.43 grams (1%) of copper powder. After thoroughly mixing the columbium-copper powder mix, the powder mix is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

The resulting pressed columbium bar is sintered under a vacuum condition of approximately 0.6 micron for 6 hours at 1800 C. The bar is then cold rolled to 60% of its thickness, following which it is re-sintered for 3 hours at 1800 C. under a vacuum condition of 0.7 micron. The resulting bar is then cold rolled to a sheet of 0.008" thickness.

Results.The bar after the second sinter contains the following impurities:

This bar is sufficiently ductile to be worked under normal conditions and is readily cold rolled to a sheet thickness of .008".

Bar 23 42.85 grams of a powder mix consisting of 90% by weight of the columbium powder and by weight of copper powder is pressed in the form of a bar under ton/in. pressure. The pressed bar has the following dimensions Thickness: Inches End 0.11 1 Center 0.114 End 0.113

Width:

End 0.633 Center 0.635 End 0.633 Length 7.5

Percent Carbon 0.003 Iron 0.023 Tungsten 0.018 TiO 0.01 SiO 0.01 Copper 0.009 Aluminum 0.020

The second sintered bar is sufiiciently ductile to be worked under normal conditions and the resulting sheet from the bar possesses excellent strength and ductility.

Bar 24 42.0 grams of a powder mix consisting of 95% by weight of the columbium powder and 5% by weight of copper powder is pressed in the form of a bar under 15 ton/in. pressure. The pressed bar has the following dimensions:

Thickness: Inches End 0.109 Center 0.115 End 0.110

Width:

End 0.635 Center 0.637 End 0.636 Length 7.5

The resulting pressed columbium bar is sintered at a temperature of 1800 C. for 6 hours under a vacuum condition of 0.7 micron. This bar is then cold rolled to 65% of its thickness and sintered a second time at a 16 temperature of 1800 C. for 3% hours under a vacuum condition of 0.6 micron. The bar is then cold rolled to a sheet of 0.008 thickness.

Results.-The bar, after the second sinter, contains the following impurities:

Percent Carbon 0.004 Iron 0.024 Tungsten 0.015 TiO 0.01 SiO 0.01 Copper 0.006 Aluminum 0.028

The bar is sufliciently ductile to be worked under normal conditions and is cold rolled to a sheet 0.008" thick.

Bar 25 32.0 grams of the columbium powder is pressed in the form of a bar under 15 tons/in. pressure. The pressed bar has the following dimensions:

Thickness: Inches End 0.255 Center 0.264 End 0.273

Width:

End 0.254 Center 0.253 End 0.255

Length 6.03

The resulting pressed columbium bar is sintered at a temperature of 1800 C. for 2 /2 hours under a vacuum condition of 0.7 micron. At the end of this period, the bar bulged and a portion melts. Upon attempting to cold roll the bar, it breaks.

Results.-Analysis of the sintered bar showed that the carbon, SiO and copper contents are reduced materially: carbon to 0.003%, SiO to about 0.2% and copper to about 0.015%. The tungsten content is reduced slightly (to about 0.019%). However, the aluminum content in the sintered bar is substantially the same as was present before sintering.

Bar 26 To 43.1 grams of columbium powder is added 0.43 gram 1%) of silver powder. After thoroughly mixing the columbium-silver powder mix, the powder mix is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

Thickness: Inches End 0.1 10 Center 0.1 1 1 End 0.109

Width:

End 0.63 6 Center 0.637 End 0.63 6 Length 7.5

Percent Carbon 0.004 Iron 0.042 'lhlngsten 0.02 TiO 0.01 SiO 0.01 Silver 0.008 Aluminum 0.042

This bar is sufliciently ductile to be worked under normal conditions and is readily cold rolled to a sheet thickness of 0.008".

Bar 27 42.9 grams of a powder mix consisting of 90% columbium powder and 10% silver powder is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

Thickness: Inches End 0.112 Center 0.114 End 0.1 10

Width:

End 0.633 Center 0.637 End 0.634 Length 7.5

The pressed bar is sintered for 6 hours at a temperature of 1805 C. under a vacuum condition of 0.7 micron. The resulting sintered bar is then cold rolled to 60% of its thickness, following which -it is re-sintered at 1800 C. for 3 hours under a vacuum condition of 0.8 micron.

Following the second sinter, the bar is cold rolled to 0.005" thickness.

Results.The bar, after the second sinter, contains the following impurities:

Percent Carbon 0.03 Iron 0.024 Tungsten 0.02 TiO 0.01 SiO 0.01 Silver 0.007 Aluminunl 0.022

The second sintered bar is sufliciently ductile to be worked under normal conditions and the resulting sheet from the bar possesses excellent strength and ductility.

Bar 28 43 grams of a powder mix consisting of 95% by weight of columbium powder and 5% of silver is pressed in the form of a bar under 15 tons/in? pressure. The pressed The resulting pressed columbium bar is sintered at 1800 C. for 6 hours under a vacuum condition of 0.7 micron. This bar is then cold rolled to 65% of its thickness and sintered a second time at a temperature of 1800 C. for 3 /2 hours under a vacuum condition of 0.6 micron. The bar is then cold rolled to 0.008 thickness.

Results.-The bar, after the second sinter, contains the following impurities:

Percent Carbon 0.004 Iron 0.025 Tungsten 0.028 Ti0 0.01 SiO 0.01 Silver 0.007 Aluminum 0.030

The bar is sufliciently ductile to be worked under normal conditions and iscold rolled to a sheet 0.008 thick.

18 Bar 29 To 43.5 grams of the columbium powder is added 0.43 grams (1%) of gold powder. After thoroughly mixing the columbium-gold powder mix, the powder mix is pressed in the form of a bar under 15 tons/in. pressure. This pressed bar has the following dimensions:

Thickness: Inches End 0.1 10 Center 0.112 Enid 0.1 1 1 Width:

End 0.636 Center 0.637 End 0.636 Length 7.5

The resulting pressed columbium bar is sintered under a vacuum condition of approximately 0.7 micron for 6 hours at 1800 C. The bar is then cold rolled to 60% of its thickness, following which it is re-sintered for 3 hours at 1800 C. under a vacuum condition of 0.7 micron. The resulting bar is then cold rolled to a sheet of 0.009" thickness.

Results.-The bar, after the second sintering, contains the following impurities:

Percent Carbon 0.004 Iron 0.042 Tungsten 0.018 TiO 0.01 SiO 0.01 Gold 0.009 Aluminum 0.030

This bar is sufficiently ductile to be worked under normal conditions and is readily cold rolled to a sheet thickness of 0.009".

Bar 30 43.0 grams of a powder mix consisting of by weight of columbium powder and 10% by weight of gold powder is pressed in the form of a bar under 15 tons/in. pressure. The pressed bar has the following dimensions:

Thickness: Inches End 0.110 Center 0.115 End 0.113

Width:

End 0.633 Center 0.635 End 0.634 Length 7.5

The pressed bar is sintered for 6 hours at a temperature of about 1800 C. under a vacuum condition of 0.8 micron. The resulting sintered bar is then cold rolled to 60% of its thickness, following which it is re-sintered at 1800 C. for 3 hours under a vacuum condition of 0.7 micron. Following the second sinter, the bar is cold rolled to 0.005" thickness.

Results.--'The bar, after the second sinter, contains the following impurities:

Percent Carbon 0.003

Iron 0.025 Tungsten 0.017 TiO 0.01 SiO 0.01 Gold 0.008 Aluminum 0.021

The second sintered bar is sufiiciently ductile to be worked under normal conditions and the resulting sheet from the bar possesses excellent strength and ductility.-

19 Bar 31 43.0 grams of a powder mix consisting of 95% by weight of the columbium powder and by weight of gold powder is pressed in the form of a bar under 15 tons/in. pressure. The pressed bar has the following dimensions:

Thickness: Inches End 0.110 Center 0.115 End 0.111

Widthz,

End 0.635 Center 0.637 End 0.635 Length 7.5

The resulting pressed columbium bar is sintered at a temperature of 1800 C. for 3 /2 hours under a vacuum condition of 0.8 micron. This bar is then cold rolled to 65% of its thickness and sintered a second time at a temperature of 1800 C. for 3 hours under a vacuum condition of 0.6 micron. The bar is then cold rolled to a sheet of 0.008 thickness.

Results.-The bar, after the second sinter, contains the following impurities:

Percent Carbon 0.003 Iron 0.025 Tungsten 0.018 TiO 0.1 l SiO 0.01 Gold 0.006 Aluminum 0.028

The bar is sufiiciently ductile to be worked under normal conditions and is cold rolled to a sheet 0.008" thick.

Bar 32 37 grams of columbium powder is pressed in the form of a rectangular-shaped bar under 55 tons/in. pressure. This columbium powder does not contain any aluminum or copper, but does contain the following impurities:

The resulting pressed columbium bar is sintered under a vacuum condition of 0.7 micron for a period of 6 hours at a temperature of 1800 C.

The bar is then cold rolled to a sheet 0.004" thick.

Results.The sintered bar contains the following impurities:

Percent Carbon 0.003 Iron 0.015 Tungsten 0.028 TiO 0.02 S10 0.03

The sintered columbium bar is sutliciently ductile to be cold rolled to foil.

It is important to note that the results of the tests conducted on Bars 1, 2, 3, 4 and 25 clearly show that the presence of a small amount of aluminum in tantalum or columbium powder, as for example 0.87% in tantalum and 1.24% in columbium, causes embrittlement of a vacuum sintered tantalum or columbium bar made from such powder and renders the resulting vacuum sintered bar non-workable under normal commercial procedures. In addition, the results of the tests conducted on Bars 1, 2, 3, 4 and 25 show that it is impossible to remove the embrittling quantity of aluminum from the pressed tantalum or columbium bar by sintering such bars under a high vacuum condition, since these bars had substantially the same amount of aluminum after sintering under high vacuum conditions as was present before sintering.

The results of the tests conducted on Bars 5 to 20, 22, 23, 24 and 26 to 31 clearly show that the addition of copper, silver or gold to tantalum or columbium powder containing an embrittling quantity of aluminum results in volatilization of the copper, silver or gold along with the embrittling quantity of aluminum from the tantalum or columbium bar during sintering to render the resulting sintered tantalum or columbium bar sutficiently ductile to be worked under normal conditions.

Having described our invention as related to the embodiments set out in the accompanying examples, it is our intention that the invention be not limited by any of the details of description unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the accompanying claims.

We claim:

1. The method of purifying tantalum powder containing as an impurity an embrittling quantity of up to about 2% of aluminum, which comprises: mixing with the said tantalum a third metal powder selected from the class consisting of copper, silver and gold; and heating the metal powder mix at a temperature of at least the sintering temperature of the tantalum, the amount of the selected third metal added being sufficient to react and volatilize 011 with the embrittling quantity of aluminum during sintering to render the sintered tantalum sufficiently ductile to be worked.

2. The method as set forth in claim 1 wherein the third metal is copper.

3. The method of purifying columbium powder containing as an impurity an embrittling quantity of up to about 2% of aluminum, which comprises: mixing with the said columbium a third metal powder selected from the class consisting of copper, silver and gold; and heating the metal powder mix at a temperature of at least the sintering temperature of the columbium, the amount of the selected third metal added being suflicient to react and volatilize ofl? with the embrittling quantity of alumi num during sintering to render the sintered columbium sufiiciently ductile to be worked.

4. The method as set forth in claim 3 wherein the third metal is copper.

5. The method of purifying tantalum containing as an impurity an embrittling amount of up to about 2% of aluminum preventing the resulting sintered metal from being sufiiciently ductile to be worked, which comprises: mixing with finely divided particles of the said impure tantalum an amount of finely divided copper, corresponding to from about 1% to about 10% by weight of the mixture; pressing the mixture into a compact; and heating the said compact at a temperature of at least the sintering temperature of the tantalum; thereby volatilizing the copper with the embrittling amount of aluminum to render the sintered tantalum sufliciently ductile to be worked.

6. The method of purifying columbium containing as an impurity an embrittling amount of up to about 2% of aluminum preventing the resulting sintered metal from being sufiiciently ductile to be worked, which comprises: mixing with finely divided particles of the said impure 21 columbium an amount of finely divided copper, corresponding to from about 1% to about by weight of the mixture; pressing the mixture into a compact; and heating the said compact at a temperature of at least the sintering temperature of the columbium, thereby volatilizing the copper with the embrittling amount of aluminum to render the sintered columbium sufficiently ductile to be Worked.

7. The method of purifying tantalum containing as an impurity an embrittling quantity of up to about 2% by weight of aluminum, which comprises: mixing with finely divided particles of the said impure tantalum an amount of finely divided particles of a third metal selected from the class consisting of copper, silver and gold corresponding to from about 1% to about 10% by weight of the mixture; pressing the mixture into a compact; and heating the said compact at a temperature of at least the sintering temperature of the tantalum, thereby volatilizing the selected third metal and the aluminum to render the sintered tantalum sufiiciently ductile to be worked.

8. The method of purifying columbium containing as an impurity an embritling quantity of up to about 2% by weight of aluminum, which comprises: mixing with finely divided particles of the said impure columbium an amount of finely divided particles of a third metal selected from the class consisting of copper, silver and gold corresponding to from about 1% to about 10% by weight of the mixture; pressing the mixture into a compact; and heating the said compact at a temperature of at least the sintering temperature of the columbium, thereby volatilizing the selected third metal and the aluminum to render the sintered columbium sufficiently ductile to be worked.

9. The method of purifying tantalum containing as an impurity from about 0.5% to about 2% by weight of aluminum, which comprises: mixing with finely divided particles of the said impure tantalum an amount of finely divided particles of a third metal selected from the class consisting of copper, silver and gold corresponding to about 1% to 10% by weight of the mixture; pressing the mixture into a compact; and heating the said compact at a temperature of at least the sintering temperature of the tantalum, thereby volatilizing substantially all of the selected third metal and the aluminum to render the sintered tantalum sufficiently ductile to be worked.

10. The method of purifying columbiun containing as an impurity from about 0.5% to about 2% by weight of aluminum, which comprises: mixing with finely divided particles of the said impure columbium an amount' of finely divided particles of a third metal selected from the class consisting of copper, silver and gold corresponding to about 1% to 10% by weight of the mixture; pressing the mixture into a compact; and heating the said compact at a temperature of at least the sintering temperature of the columbium, thereby volatilizing substantially all of the selected third metal and the aluminum to render the sintered columbium sufliciently ductile to be worked.

11. Themethod of purifying tantalum containing as an impurity an embrittling quantity of up to about 2% by weight of aluminum, which comprises: mixing with finely divided particles of the said impure tantalum an amount of finely divided particles of a third metal selected from the class consisting of copper, silver and gold corresponding to from about 1% to about 10% by weight of the mixture; and heating the said mixture at a temperature of at least the sintering temperature of the tantalum, thereby volatilizing the selected third metal and the aluminum to render the sintered tantalum sufiiciently ductile to be worked.

12. The method of purifying columbium containing as an impurity an embrittling quantity of up to about 2% by weight of aluminum, which comprises: mixing with finely divided particles of the said impure columbium an amount of finely divided particles of a third metal selected from the class consisting of copper, silver and gold corresponding to from about 1% to about 10% by weight of the mixture; and heating the said mixture at a temperature of at least the sintering temperature of the columbium, thereby volatilizing the selected third metal and the aluminum to render the sintered columbium sufiiciently ductile to be worked.

13. The method of purifying a refractory metal containing as an impurity an embrittling quantity of up to about 2% by weight of aluminum, which comprises: mixing with finely divided particles of the said impure refractory metal an amount of finely divided particles of a third metal selected from the class consisting of copper, silver and gold corresponding to from about 1% to about 10% by weight of the mixture; and heating the said mixture at a temperature of about the sintering temperature of the refractory metal, thereby volatilizing the selective third metal and the aluminum to render the refractory metal suificiently ductile to be worked.

14. The method of purifying a refractory metal powder containing as an impurity an embrittling quantity of up to about 2% of aluminum, which comprises: mixing with the said refractory metal powder a third metal powder selected from the class consisting of copper, silver and gold; and heating the metal powder mix at a temperature of about the sintering temperature of the refractory metal, the amount of the selected third metal added being suflicient to react and volatilize off with the embrittling quantity of aluminum during heating to render the refractory metal sufficiently ductile to be worked.

15. The method of purifying a powdered refractory metal selected from the class consisting of tungsten, molybdenum, tantalum and columbium containing as an impurity an embrittling quantity of up to about 2% of aluminum, which comprises: mixing with the selected powdered refractory metal a third metal powder selected from the class consisting of copper, silver and gold; and heating the metal powder mix at a temperature of about the sintering temperature of the selected refractory metal, the amount of the selected third metal added being suflicient to react and volatilize off with the embrittling quantity of aluminum during heating to render the refractory metal sufficiently ductile to be Worked.

No references cited. 

1. THE METHOD OF PURIFYING TANTALUM POWDER CONTAINING AS AN IMPURITY AN EMBRITTLING QUANTITY OF UP TO ABOUT 2% OF ALUMINUM, WHICH COMPRISES: MIXING WITH THE SAID TANTALUM A THIRD METAL POWDER SELECTED FROM THE CLASS CONSISTING OF COPPER, SILVER AND GOLD; AND HEATING THE METAL POWDER MIX AT A TEMPERATURE OF AT LEAST THE SINTERING TEMPERATURE OF THE TANTALUM, THE AMOUNT OF THE SELECTED THIRD METAL ADDED BEING SUFFICIENT TO REACT AND VOLATILIZE OFF WITH THE EMBRITTLING QUANTITY OF ALUMINUM DURING SINTERING TO RENDER THE SINTERED TANTALUM SUFFICIENTLY DUCTILE TO BE WORKED. 